1. Field of the Invention
The present invention relates to a vibration damping system for an engine mounted on a vehicle.
2. Description of the Related Art
An engine is conventionally mounted on vehicle frames through mounting elements including rubber cushions or the like as components, thereby to restrain vibrations from being transmitted from the engine to the frames. Various constructions and arrangements of the mounting elements for absorbing the vibrations have been proposed, and one example thereof is disclosed in U.S. Pat. No. 6,374,939.
The mounting elements employed in the U.S. patent may, with some effect, restrain engine vibrations from being transmitted to the frames. However, such a construction does not positively restrict the vibrations of the engine per se, and thus has no effect for restraining airborne noise produced by the engine vibrations. Thus, some specific design is required to restrict the vibrations of the engine per se in order to restrain such noise. To this end, active damping systems have begun to be proposed, but such systems still have a serious problem of large-scale construction and control as well as increased cost.
Further, the vibrations of the engine per se could be increased depending on the elasticity of the mounting elements, and also the damping effect achieved by the mounting elements is limited. Especially, with a diesel engine having a small number of cylinders mounted on a small vehicle such as an agricultural tractor, it has been difficult to restrain engine vibrations and resulting noise generation solely by the mounting elements.